POTENTIAL 2070 IMPLICATIONS OF SEA-LEVEL RISE AND CHANGING RAINFALL FOR WATER TABLES AND SALTWATER INTRUSION IN SELECTED AREAS OF MIAMI-DADE COUNTY FLORIDA

We produced an updated version of the integrated surface/groundwater model developed by the United States Geological Survey—the Urban Miami-Dade Model—to evaluate changes in water table position and seawater intrusion 50 years into the future. This is the most comprehensive model known to exist at the scale of the entire urban portion of the County (4000 km²). The model utilizes the sharp-interface Saltwater Intrusion package (SWI2) and a surface water routing model (SRW1) designed to simulate the region’s extensive canal system and its water level control structures.

Updates to model inputs included: (a) ocean boundary conditions; (b) future rainfall patterns; (c) Everglades water levels; (d) changes to the northern and southeastern model boundaries; and (e) potential change in land use and corresponding changes in impervious areas and changes to aquifer properties in areas with new quarry lakes. Future ocean boundary conditions reflecting sea level rise were based on the U.S. Army Corps of Engineers High curve. Future rainfall was estimated with bias-corrected results from the Localized Constructed Analogs data set. Future Everglades water levels on the western boundary of the model are expected to be higher due to continuing implementation of the Comprehensive Everglades Restoration Plan (CERP). We applied simulated Everglades water levels for the full-CERP implementation (CERP0) scenario produced by the South Florida Water Management District, which includes projected future land use, historical rainfall, and CERP restoration components such as partial decompartmentalization of a large water conservation area and Everglades National Park, Lakebelt Storage, etc.

We examine model results in five sub-regions that range in size from 1.5 to 25 km². These areas include: the South Beach portion of the City of Miami Beach, the City of Surfside, the Town of Cutler Bay, the Arch Creek area, and the Turkey Point Nuclear Plant cooling canals. Water tables are expected to rise more than 0.5 m between 2010 and 2070 in many areas, consistent with a 0.9-m rise in sea level, and frequently leading to a loss of one-third or more of the current vadose zone. Inland and vertical movement of the saltwater front is variable in the different sub-regions, with up to 2 km inland movement and 10 m rise.